Pyrrhotite Re-Os and SHRIMP zircon U-Pb dating of the Hongqiling Ni-Cu sulfide deposits in Northeast China

摘要

The Hongqiling (HQL) magmatic Ni-Cu sulfide deposits (Jilin Province, NE China) are located at the southern margin of the eastern Xing'an-Mongolian Orogenic Belt (XMOB) of the eastern Central Asian orogenic belt (CAOB), situated between the Siberian Craton (SC) and the North China Craton (NCC). The HQL ore-bearing mafic-ultramafic intrusions intrude into the metamorphic rocks of the lowermost Huangyingtun Formation of the Hulan Group (HLG), whose lithology is herein identified as a hornblende-zoisite gneiss. SHRIMP zircon U-Pb dating for the HLG, country rock of the HQL deposits, indicated a maximum deposition age of 272.2 ± 4.3 Ma (95% confidence level, MSWD = 2.6, n = 14).Six pyrrhotite samples separated from massive Ni-Cu sulfide ores of the Fujia (No. 7) deposit yielded a Re-Os isotopic isochron age of 208 ±21 Ma (95% confidence level, MSWD=2.4, n = 6), indicating that the ore-formation age was Late Triassic. Re-Os isotope analyses showed an initial ~(187)Os/~(188)Os ratio of 0.315 ± 0.050. The γ_(Os) values ranged from +137 to +161 with an average of +151, indicating that its ore-forming materia Is were mainly derived from mantle with possibly <30% crustal Os contamination. Large scale magmatic Ni-Cu mineralization in eastern Jilin occurred in post-collisional tectonic setting in the Late Triassic Our new results suggest that the ages of the Ni-Cu sulfide deposits in the CAOB within China tended to become younger from west to east, as manifested by the Late Caledonian (-440 Ma), through the Late Hercynian (300-265 Ma) to the Late Indosinian (225-200 Ma). Such variation could reflect the gradual closure and post-collisional orogeny between the SC and the NCC from west to east.